The present invention relates to microwave/Direct Current (DC) power converters employing fast cyclotron wave of the electron beam. The microwave/DC power converters may be used as a receiver in a microwave energy transmission (MET) system or a wireless power transmission (WPT) system.
In connection with successful developing ideas of WPT during the last several decades, there appeared a new problem, namely, the problem of back conversion of high power microwave energy into the energy of direct current (DC). It is not impossible that in future microwave technology will find its wide scale application in this field.
Well-known rectennas (rectifying antennas) with Schottky-diodes have played and play a fundamental role at the stage of principal demonstration of the possibilities of highly efficient wireless power transmission by microwaves. However, they become not so attractive for future real high power industrial WPT systems, because of some essential problems as:
low power level of single rectenna element;
low output voltage and therefore, necessity to connect diodes in series; and
high level of breakdown possibility being dangerous even at rather small levels of microwave or DC overloads.
Industrial energy systems always demand and use high power and high voltage devices to decrease losses and to increase reliability.
The most studied cyclotron wave converter (CWC) is shown in FIG. 3A (Vladimir A. Vanke et al., xe2x80x9cCyclotron Wave Converter of Microwaves into DCxe2x80x9d, IEICE Trans. on Electronics (Japan), Vol. E81-C (1998), No. 7 (July), p.1136). The CWC 30 comprises an electron gun 31, a microwave cavity 32, a collector 33 and a transition space 34 aligned on the z-axis. The microwave cavity 32 usually called xe2x80x9cCuccia couplerxe2x80x9d includes a gap of interaction and is subjected to a static and uniform magnetic field with the magnetic flux density B1 in the direction of z created by an external static magnetic field generator (not shown). The transition gap 34 is subjected to another external static magnetic field with the magnetic flux density B2 in the direction of -z.
When microwave power P of frequency F is input into the microwave cavity 32 of the CWC 30, the microwave power P creates a transverse electric field alternating at the frequency F in the interaction gap 35 of the microwave cavity 32. As the electron gun 31 generates a flow of electrons and the electron beam is sent into the center of the interaction gap 35 by an electron lens, the electron beam rotates at the frequency F (equal to the cyclotron frequency Fc) due to the alternating transverse electric field in the gap 35.
In the transition region 34, the rotating electron beam receives additional Lorenz forces due to existing of the radial component of the reversed static magnetic field (z1 less than z less than z2 in FIG. 3B) and because of it the tangential component of the velocity of the electron beam decreases and the z component of the velocity of the electron beam increases.
The z-accelerated electron beam 36 enters the collector 33, where the kinetic energy of the electron beam is extracted as a DC power in the load-resistance 37.
CWC is potentially powerful and already tested at power level of 10 kW, which is rather well known from the previous different publications, in particularly from patents U.S. Pat. No. 3,462,636 and RU 2,119,691.
However, such type of CWC demands high intensity of static magnetic field that corresponds to the cyclotron frequency equal to the frequency of external microwave power source. This requirement usually creates essential technical problems, especially in the short centimetric and millimetric wavebands.
The present invention uses two microwave cavities having uniform and 2n-pole (where n=2, 3, . . . ) electric fields in the interaction gaps, which makes it possible to reduce the magnetic field intensity into half (if n=2) or less.
According to the present invention, a microwave/DC power converter includes: an electron source for generating a beam of electrons running on an axis; a group of 2n (where n=2, 3, . . . ) rod electrodes aligned symmetrically in parallel around the axis for receiving an externally supplied microwave power and for giving the electron beam a rotational movement around the axis according to the microwave power; and a converter for converting the energy of the movement of the electron beam into the energy of a DC current.
In a second form of the present invention, a microwave/DC power converter includes: an electron source for generating a beam of electrons running on an axis; a first microwave cavity for giving the electron beam an initial rotational movement; a second microwave cavity including a group of 2n (where n =2, 3, . . . ) rod electrodes aligned symmetrically in parallel around the axis for receiving an externally supplied microwave power and for giving the electron beam a cyclotron movement around the axis according to the microwave power; a kinetic converter for converting the cyclotron movement of the electron beam into an axial movement; and a current converter for converting the energy of the axial movement of the electron beam into the energy of a DC current.
In the above microwave/DC power converter, the first microwave cavity may preferably include a phase shifter for adjusting a phase of a rotational position of the electron beam with respect to the rod electrodes when the electron beam enters the second microwave cavity.
The microwave/DC power converter may further include a resistance, which is provided between the electron source and both the first microwave cavity and the second microwave cavity in order to prevent an over current.
The microwave/DC power converter may further include an auxiliary electrode provided before the current converter, where a voltage applied on the auxiliary electrode is set slightly lower than a voltage applied on the current converter.
Since, in the microwave power converter of the present invention, the interaction of the electric field and the electron beam is operated at the cyclotron frequency one n-th of that of conventional converters, the static magnetic field can be substantially reduced. It makes possible to create a compact, powerful and efficient microwave/DC power converter.